JP2840041B2 - Electrostatic chuck - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates generally to electrostatic chucks used to secure semiconductor wafers in a processing chamber and, more particularly, to increasing the cooling of a wafer and the effectiveness of such chucks. It is a significant improvement that extends the life.

[0002]

2. Description of the Related Art Electrostatic chucks are used in semiconductor processing chambers to hold individual semiconductor substrates or wafers on a chamber pedestal. Electrostatic chucks typically include a dielectric layer and electrodes. When a semiconductor wafer is placed in contact with a dielectric layer and a direct current (dc) voltage is applied to the electrodes, an electrostatic attraction is generated to attract the wafer to the chuck.
This type of chuck is particularly useful in a vacuum processing environment where the differential pressure holding the wafer in place is insufficient or mechanical fixing of the wafer is undesirable. One processing environment in which electrostatic chucks are widely used is a plasma etching process.

[0003] Electrostatic chucks are formed using only a single dielectric layer and electrodes, but a more typical structure is a thin copper layer, preferably sandwiched between upper and lower dielectric layers or an organic material such as polyimide. It includes a thin laminated member having an electrode core that is a layer. To assemble these layers into one laminated sheet and attach the laminated sheet to the chamber pedestal,
A polyimide adhesive may be used.

The upper and lower polyimide layers merge at the perimeter edge of the electrode to prevent exposure of the copper electrode to the processing chamber, which typically contains a plasma that damages the copper layer. In operation, the copper electrode is connected to a voltage source and functions as an anode. The operating principle of the electrostatic chuck is well known and is not important to the present invention. It is sufficient to note that the electric field formed on the pedestal creates a mutual attractive force between the pedestal and the semiconductor wafer placed in contact with the laminate.

[0005]

Many of the processes that wafers undergo generate heat, and measures must be taken to cool the wafer to an acceptable processing temperature to prevent thermal damage. In most prior art electrostatic chucks, helium gas is introduced beneath the wafer through a central opening in the pedestal and then distributed through the channel of the laminate on the pedestal. Various groove forms have been used in an effort to distribute the cooling gas uniformly across the wafer surface, which is usually circular. A disadvantage with this cooling method is that it prevents uniform cooling near the edge of the wafer. If the groove extends to the edge of the wafer, especially near the edge, the rate of gas leakage is high and the cooling effect is reduced. In most designs, the groove ends before reaching the edge. In one design,
A radial groove is adjacent to the second groove near the edge, the second groove extending peripherally a short distance before the end, or a branch groove extending in various directions before the end. Take shape. However, all of these designs still have undesirable overheating near its peripheral edge of the wafer.

[0006] Another disadvantage of the prior art electrostatic chucks stems from the method by which polyimide and copper laminates are formed on the chuck pedestal. The first of polyimide
A layer is placed on the pedestal, then a copper electrode is placed on the polyimide. Naturally, the copper layer cannot extend to the polyimide edge because the polyimide layer provides a seal around the outer edge of the copper. When the second polyimide layer is disposed over the copper layer, the overall thickness of the laminate is less around the polyimide edge (thickness of the polyimide two layers) than the overall laminate thickness including the copper layer. . Therefore, the laminate has an annular step outside the outer diameter of the copper layer. This annular step has two detrimental effects on the performance of the electrostatic chuck. First, only a very small area of the chuck is in contact with the wafer beyond the outer diameter of the copper layer due to this step. As a result, there is a high probability of helium leakage at the edge of the wafer and there is undesired overheating of the edge area of the wafer. A second effect of the annular steps of the laminate structure is that the outer edge of the copper layer is insulated from the hazardous chamber environment only by a very thin polyimide layer having about the same thickness as the polyimide top layer. If this layer is eroded by the processing plasma in the chamber, the chuck must be replaced. Polyimides and other organic materials have relatively low tolerance for many process gases and plasmas.
Therefore, placing a good insulating layer around the electrodes is an important issue.

[0007] From the foregoing, it will be appreciated that there is a need for an improved electrostatic chuck. What is particularly needed is an improved chuck structure that increases cooling near the edge of the wafer and increases the useful life of the chuck. The present invention satisfies this need, as will be apparent from the following description.

[0008]

SUMMARY OF THE INVENTION The present invention provides a significant improvement between a wafer and a chuck, particularly at the edge of the chuck, by distributing cooling gas through the chuck at multiple points across the chuck pedestal surface. The present invention relates to an electrostatic chuck that provides heat transfer. Further, the chuck of the present invention exhibits a flat surface to the wafer to the edge of the laminate mounted on the chuck pedestal, thereby further improving the cooling of the wafer edge and extending the useful life of the chuck. .

[0009] Briefly and generally speaking, the electrostatic chuck of the present invention comprises a pedestal for supporting a workpiece.
A laminated plate including an insulated copper electrode mounted on the pedestal and having a processed member fixed to the laminated plate when a voltage is applied to the copper electrode;
And a plurality of holes extending upwardly through the pedestal and the laminate for delivering gas to cool the workpiece from below, wherein many of the holes are located near the outer periphery of the workpiece. Including. The pedestal also includes a cooling gas reservoir formed beneath the pedestal and extending across all holes and a cooling gas supply to the reservoir. The hole preferably tapers to a small diameter at the upper end.

[0010] More specifically, the laminate comprises a first insulating layer; a copper electrode layer formed on the first insulating layer; and a first insulating layer formed on the copper electrode and around an edge of the copper electrode layer. And a second insulating layer that insulates the copper from the processing environment in which the electrostatic chuck is mounted. According to one aspect of the invention, the second insulating layer exhibits a substantially flat upper surface over the entire width of the laminate. Thereby, good contact with the workpiece is maintained beyond the outer edge of the copper electrode. Further, the copper electrodes are widely separated from the effects of the processing plasma, extending the useful life of the electrostatic chuck.

To achieve this flat top surface, the pedestal has a groove formed in its top surface. Therefore, the first
The insulating layer mates with the groove when placed on the pedestal. FIG. 4 shows a composite top surface in which copper electrodes substantially fill the trenches and are substantially flat and covered with a second insulating layer. FIG.

The electrostatic chuck of the present invention also includes a pedestal for supporting a semiconductor substrate; and a laminated plate including an insulated copper electrode mounted on the pedestal. When a voltage is applied to the copper electrode, the substrate is placed on the laminated plate. It is more specifically defined to be electrically fixed. The laminate comprises a first dielectric layer; a copper electrode layer formed on the first dielectric layer; and an electrostatic chuck formed on the copper electrode and fused with the first dielectric layer around an edge of the copper electrode layer. A second dielectric layer insulates the copper from the attached processing environment. The second dielectric layer exhibits a substantially flat top surface over the entire width of the laminate, thereby maintaining good contact with the substrate beyond the outer edge of the copper electrode. Furthermore,
Copper electrodes are widely separated from the effects of the processing plasma to extend the useful life of the electrostatic chuck.

With respect to the novel method, the present invention forms a shallow groove having a depth equal to the thickness of the electrode at the top of the pedestal; disposing a first dielectric layer across the pedestal;
Disposing an electrode layer over the dielectric layer so that the electrode layer coincides with a shallow groove; disposing a second dielectric layer across the first dielectric layer and the electrode layer to form a relatively flat surface Is included. The electrode layer is then effectively shielded from the processing environment by relatively long insulating paths, so that the flat surface makes good contact with the substrate in areas outside the outer edges of the electrodes.

From the foregoing, it will be appreciated that the present invention represents a significant advance in the field of electrostatic chucks. In particular, the present invention provides a chuck in which the overheating of the edge is actually removed and the temperature gradient is dramatically reduced. Furthermore, the structure of the stack of members of the chuck provides good contact with the wafer around its outer area and prolongs the useful life of the chuck.

[0015] Other aspects and advantages of the present invention will become apparent from the following detailed description, taken in conjunction with the drawings.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS As shown in the accompanying drawings, the present invention relates to an improvement in an electrostatic chuck. As shown in FIGS. 1 and 2, a typical electrostatic chuck includes a pedestal indicated by the numeral 10 on which a multilayer laminate 12 (to be described) is mounted. Pedestal 1
A central opening 13 in 0 extends upwardly through the laminate 12 and communicates with a plurality of grooves 14 extending radially across the laminate 12 from the central opening. The pedestal 10 is shown fixed to the pedestal base 15 with screws 16.
An annular insulating collar 17 is mounted on the pedestal. The top of the pedestal 10 and the laminate 12 are usually circular so as to match the contour of the semiconductor wafer 18 located on the laminate. As best shown in FIG. 4, the laminate 12 comprises a polyimide underlayer 20,
It includes a copper electrode layer 22 and a polyimide upper layer 24. The polyimide upper layer 24 and the lower layer 20 around the edge of the copper layer 22 and the groove 1 shown in FIG.
4. Fuse and seal along each of the four.

FIGS. 3A and 3B show another groove structure used in the past. In the structure of FIG. 3 (a), each of the radial grooves 14 merges with an arcuate or partially annular groove 14 'extending around the laminate 12 to the vicinity of its periphery. In the structure of FIG. 3 (b), each of the radial grooves 14 is adjacent to an additional groove branch 14 "and extends in different directions towards the periphery of the laminate. These and other structures include: All attempts to provide sufficient cooling gas near the edge of the wafer 18 without placing grooves near the edge where excessive cooling gas leakage occurs.All of these structures have a common drawback: wafer edge area. In all cases, there is little heat transfer and static pressure in the groove area and there is a large temperature gradient at the wafer edge.

Another notable disadvantage of the prior art electrostatic chuck is shown in FIG. 7, which details the edge area of the laminate 12 and wafer 18. Laminate 12 first places polyimide lower layer 20 on pedestal 10, then places copper electrode layer 22 on lower polyimide layer, and finally forms polyimide upper layer 24 on first two layers 20 and 22. It is made by doing. Inevitably, this structure requires that the polyimide top layer 24 and the wafer 18 be formed because the thickness of the two polyimide layers is less than the total thickness of the two polyimide layers and the copper layer.
And an annular gap remains. This laminated structure has two detrimental effects. First, since the wafer 18 is not supported by the laminate 12 in the region of the gap 30, there is only a very small range of wafer-to-laminate contact beyond the outer diameter of the copper layer 22. There is no electrostatic chucking force generated beyond the outer edge of copper layer 22. Thus, cooled helium gas supplied at a few Torr pressure up to 20 Torr leaks into the processing chamber beyond this small range. Due to the leakage of the cooling gas, the gas pressure decreases and the temperature near the wafer edge increases. The size of the copper electrode 22 is the size of the pedestal 10 and the minimum overlap of the polyimide layers 20 and 24 (about 1.5
mm).

A second detrimental effect of the annular gap 30 is that the minimal insulation of the copper exhibited by the laminate is limited to the outer edge of the copper layer 22 and the annular gap 3 because the processing plasma is present in the gap.
It is a distance 31 between 0. In known chucks, this distance is close to the thickness of one of the polyimide layers, about 0.025-
It is 0.050 mm. This small insulation thickness results in a relatively short effective service life of the chuck.

According to one important aspect of the present invention, FIG.
As shown, the laminate 12 is formed to exhibit a flat top surface that extends well from the outer diameter of the copper layer 22. In particular, the copper layer 22 'is embedded in the polyimide layer 20', these two layers exhibiting a flat surface on which the polyimide upper layer 24 'is formed. One method of embedding the copper layer 22 'in an appropriate amount is to use the copper electrode 22' by about 0.1-0.2 mm.
First, an annular groove is formed in the upper surface of the pedestal 10 by machining a counterbore of a diameter selected to be larger than the diameter of the pedestal 10. The depth of the groove is the copper electrode 22 '.
Is about 0.040 mm. Then, the polyimide lower layer closes the groove of the pedestal 10, leaving a groove corresponding to the upper surface of the polyimide lower layer, and the copper layer 22 'is disposed therein.

This structure overcomes the shortcomings of the prior art discussed as FIG. In particular, since the laminate 12 exhibits a top surface that is sufficiently flat from the outer diameter of the copper layer 22 ', the outer area of the wafer 18 has a large contact surface with the laminate and reduces edge leakage. Also, the annular gap of FIG. 7 has been removed in FIG. 8 to increase the minimum insulation thickness between the copper layer 22 'and the plasma to about 1.5 mm, or more than 30 times. Therefore,
The useful life of the chuck is significantly extended and its processing performance is improved.

Another important aspect of the present invention is the use of multiple openings to introduce cooling gas to the underside of wafer 18. This is best illustrated in FIGS. 5 and 6, where the pedestal 34 includes a coolant reservoir extending across the bottom of the pedestal and is formed in part by a circular plate 38 secured to the pedestal with screws 40. . Cooling gas is provided in a single passage 42 at one end of the reservoir.
Through the reservoir 36 and an O-ring 44 seals the reservoir. A plurality of holes 46 are formed in the upper surface through the pedestal. Holes in corresponding locations (not shown) are also formed in the laminate as grooves were formed in prior art structures. (See FIG. 4.) There are about 100-200 holes, many of which are located close to the edges of laminate 12. The hole 46 has a small diameter, for example, 0.25-
It is preferably 0.50 mm and tapers to a smaller diameter at the upper or outlet end.

The prototype test of the present invention in the tungsten etchback step reduced the overall temperature of the wafer by about 10 ° C and reduced the wafer edge temperature from 80 ° C to about 60-65 ° C. In addition, the temperature gradient between the center of the wafer and its edge was reduced from 15-20C to 6-10C. Contrary to the disadvantages associated with overheating in prior art electrostatic chucks, repetitive and acceptable process results have been obtained with the chuck of the present invention.

Test results on the prototype of the present invention indicate that if the electrostatic chuck provided sufficient thermal conductance and a sufficient helium supply to leak to the wafer edge, the wafer edge would be considered excessive in prior art chucks. It is clear that the leakage of helium is not detrimental to the process. For example, edge leakage in prior art chucks is about
Although 0.2-1.0 sccm (standard cubic centimeters per minute), the presence of a 2-5 sccm leak at 9 torr pressure in the chuck of the present invention had no detectable effect on the process. Most leakage was from holes near the wafer edge. Blocking these holes reduced leakage by a factor of about 10, or 0.4-0.6 sccm, but resulted in overheating of the wafer edge and loss of selectivity.

[0025]

According to the present invention, since the present invention is constructed as described above, it is possible to efficiently cool the entire surface of the wafer, particularly over the edge, to improve the fixing action at the edge and the wafer contact,
Effective product life can be extended.

[Brief description of the drawings]

FIG. 1 is a plan view of a prior art electrostatic chuck showing radial cooling grooves emanating from a central cooling supply passage in a chuck pedestal.

2 is a cross-sectional view of the prior art of FIG. 1 substantially along 2-2.

FIG. 3 is a plan view of a conventional electrostatic chuck, showing two types of cooling groove structures (split diagrams (a) and (b)).

FIG. 4 is a fragmentary, enlarged cross-sectional view of a prior art electrostatic chuck showing a portion of a laminated polyimide and copper layer formed on a chuck pedestal.

FIG. 5 is a plan view of an electrostatic chuck according to the present invention, showing a plurality of cooling holes formed in a chuck pedestal.

FIG. 6 is a cross-sectional view of the electrostatic chuck of FIG. 5 substantially along 6-6.

FIG. 7 is a fragmentary cross-sectional view of a prior art electrostatic chuck showing how a laminate of polyimide and copper layers is formed on a chuck pedestal substantially along line 7-7 of FIG. .

FIG. 8 is a fragmentary sectional view similar to FIG. 7, but showing a structure according to the invention.

[Explanation of symbols]

10 pedestal, 12 laminated board, 13 central opening, 1
4, 14 '... groove, 16 ... screw, 17 ... insulating joint ring, 18
... Semiconductor wafer, 20 ... Polyimide lower layer, 22 ... Copper electrode layer, 24 ... Polyimide upper layer, 30 ... Gap, 31 ... Distance,
34 pedestal, 38 circular plate, 40 screw
42 ... single passage, 44 ... O-ring, 46 ... hole.

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Shamoyl Chamoyrian United States, California 95120, San Jose, Washoe Drive 1256 (72) Inventor Manuture Billang United States of America, California 95036, Los Gatos, Fabre Ridge Road 18836 (72) ) Inventor Alfred Mac 32722, Union City, Union City, CA 94587, United States 32722 (72) Inventor Simon Double. Tam, United States, 95035, California, Milpitas, Oregon Way 1001 (56) References JP-A-4-253356 (JP, A) JP-A-5-121530 (JP, A) JP-A-6-244144 (JP, A) (58) Field surveyed (Int. Cl. ⁶ , DB name) H01L 21/68

Claims (3)

(57) [Claims] A pedestal having a substantially flat upper surface for supporting a processing member, a laminated plate including an insulated electrode layer, wherein the laminated plate is mounted on the pedestal and a voltage is applied to the electrode layer. The work piece is electrostatically secured to the laminate when applied, and extends upward through the pedestal and the laminate to send a gas to cool the work piece from below. A plurality of holes, many of which are located near an outer periphery of a work piece; wherein the pedestal is formed below the pedestal and extends across all holes. Wherein the pedestal includes a cooling gas reservoir and a cooling gas supply port to the reservoir, and wherein the pedestal has a recess formed in an upper surface thereof except an outer edge portion; A first insulating layer extending over substantially the entire upper surface of the pedestal in a state following the recess; and a portion of the first insulating layer following the recess is substantially buried and disposed on the first insulating layer. A second insulating layer extending over the electrode layer and a portion of the first insulating layer that is not covered by the electrode layer; wherein the second insulating layer substantially covers the entire surface of the laminate. A flat top surface, whereby good contact with the workpiece is maintained beyond the outer edge of the electrode layer, and the electrode layer is widely separated from the influence of the processing plasma to prolong the useful life of the electrostatic chuck. Electrostatic chuck. 2. A pedestal having a substantially flat upper surface for supporting a semiconductor substrate; and a laminated plate including an insulated electrode layer, wherein the laminate is formed on the pedestal, and a voltage is applied to the electrode layer. The laminate in which a processing member is electrostatically fixed to the laminate;
An electrostatic chuck including: wherein the pedestal has a recess formed on an upper surface thereof excluding an outer edge portion, and in a state where the laminate follows the recess on the upper surface of the pedestal,
A first insulating layer extending substantially over the entire upper surface of the pedestal; an electrode layer disposed on the first insulating layer substantially filling a portion of the first insulating layer following the recess; A second insulating layer extending to the electrode layer and a portion of the first insulating layer not covered by the electrode layer; wherein the second insulating layer has a substantially flat upper surface over the entire surface of the laminate. Thus, an electrostatic chuck that maintains good contact with the processing member beyond the outer edge of the electrode layer, and extends the effective life of the electrostatic chuck by separating the electrode layer from the influence of processing plasma particles. 3. A method for manufacturing an electrostatic chuck having a laminated member having an insulated electrode layer and a pedestal, wherein an upper portion of the pedestal except an outer edge portion has a thickness substantially equal to a thickness of the electrode layer. Forming a shallow recess having a depth; arranging a first dielectric layer on the substantially entire surface of the pedestal following the recess; arranging the electrode layer on the first dielectric layer; Filling the recesses of the first dielectric layer with the electrode layer; forming a substantially flat surface by disposing a second dielectric layer on substantially the entire surface of the first dielectric layer and the electrode layer; Including methods.